The invention relates to a block or sucker for a machine used to grind or to machine the edge and possibly the optical surfaces of eyeglass lenses and a process for eyeglass grinding or machining ( for plastic lenses a milling machine may be used).
If an optician is to process a pair of eyeglass lenses on the basis of the optical values for the eyeglass lenses given him by the customer, optometrist or ophtamologyst and on the basis of the eyeglass frame selected by the customer, he can order the eyeglass lenses with the prescribed optical values from a manufacturer of eyeglass lenses. Generally the optician keeps keeps a large number of eyeglass lenses of different optical values in stock. This applies to both glass and plastic lenses. The optician then machines the edges in accordance with the frame selected, mounts the finished eyeglass lenses in the eyeglass frame and delivers the finished eyeglasses to the customer.
Blocks made of a metal alloy with a low melting temperature can be used in such eyeglass lens grinding machines. However, these blocks are generally made of plastic. Alternatively suckers can be use. These blocks or suckers have a relatively small diameter, generally smaller than the shortest distance between the edge of the finished eyeglass lens and the optical center of the lens in order to avoid these blocks or suckers protruding into the operating range of the tool used to machine or grind the edge of an eyeglass lens.
In order to reduce the inventory of finished or semi-finished eyeglass blanks which is required to be maintained by an optician to a minimum a practice has recently become popular whereby an inventory of pressed eyeglass lens blanks is only maintained, the major surfaces of which are essentially parallel and one of which surfaces may already be finished. Such semi-finished eyeglass blanks have their optical surfaces machined in accordance with the optical values transmitted by the optician and in response to the order by the optician, whereafter they are delivered to the optician who then performs the edging process. This machining of the optical surfaces is carried out by businesses specialized in this work, on order, so that the need by the optician to maintain an inventory of eyeglass lenses, the optical surfaces of which are finished is dispensed with.
When machining the optical surfaces of an eyeglass lens blank, in contradistinction to finishing the edge the eyeglass lens blank, this operation requires the blank to be held by means cf a block or a sucker interfacing with only a single major surface so that the other major surface is exposed for machining. Such a block or sucker will usually have a diameter which is approximately equal to the diameter of the eyeglass lens blank since the holder for the eyeglass lens must have great strength and stiffness in order to absorb the forces engendered during the machining of the optical surfaces.
A block made of a metal which has a relatively low melting temperature is often used in contacting the optical surfaces. This block is cast on the eyeglass lens blank and adheres firmly to the glass while at the same time exhibiting sufficient strength to be attached securely and without rocking to a holder in the machine for processing the optical surface.
Blocks made of a metal with a low melting temperature can also be used when processing plastic eyeglass lenses. In this case a self-adhesive intermediate film is applied to the plastic eyeglass lens blank and the block is cast on this film. The block can also be made of plastic and be attached to the eyeglass lens blank by vacuum action or with an adhesive.
Once machining of the optical surfaces has been completed the block or sucker used for this purpose is detached from the eyeglass lens and the eyeglass lens is delivered to the optician for edging. In the latter process a block or sucker of appropriately smaller diameter and suitable for edging is again attached to the eyeglass lens blank.
The foregoing description illustrates that the complexity of the work needs to be carded out. Such for work is tedious for an optician in both cases, since he will basically have to order the eyeglasses in advance with the prescribed optical values and then fit the eyeglass lenses received with a block or sucker. The latter must be adjusted in accordance with the optical values and in particular in accordance with the angle of the axis of the cylinder (cylinder angle). Such adjustment of the eyeglass lens in the eyeglass frame is effected in relation to the interpupillary distance of the person who has selected the glasses. Only then can the machining of the eyeglass lens edge be carried out.
In German published, unexamined patent application No. 15 77 502, on the other hand, a machine is described for processing the optical surfaces and the edge of eyeglass lenses using one and the same cast-in-place block made of a metal alloy with a low melting temperature. This block must however exhibit such a small diameter or must be reduced to such a diameter after the machining of the optical surfaces that the outside surfaces of the block do not come into contact with the edging tool and do not interfere with the edging process. Basically, however, the diameter of the block will from the very outset be smaller than normal, so that there will be an adverse influence on the guidance accuracy during machining of the optical surfaces.